VARIATIONS OF GAETER-SNAKES. 



115 



hand, is more variable than in either of the other forms in the fjroup. 

 An examination of the diagrams (figs. 46-47) will show that the 

 variation in both series consists of a loss or an addition of one scute 

 from the more constant number 7/10. The average number of 

 supralabials is generally a little above 7, showing the comparative 





13 



- - -/^-- ~ -" 



^Y^-^ 



10 



Avoca, Washing- Delaware Khode 

 North ton,D.C., County, Island, 

 Carolina. Laurel, Pennsyl- Massa- 



Pig. 40.— Diagram showing the variation in the number of supralabials in Thamnophis 



sauritus. 



rareness of specimens with 8 or 6 scutes in this series. No definite 

 geographic differences can be discovered in the material examined. 

 In the case of the infralabials the conditions are exactly reversed in 

 that, while the variations are so slight as to disturb the averages 



n 



10 



r" 3 



u 



u 



4.. 



--)(--- 



->: — 



10 



but little, the differences that do occur are mostly by way of a 

 reduction to 9, so that the averages run a little below 10. 



As in the other ribbon snakes, the variation in the number of 

 ventral plates is considerable. In the material examined the ex- 

 tremes are 150 and 172. The table (fig. 48) will show how the 



